1. Field of the Invention
The present invention relates to a vertical gallium nitride-based light emitting diode (hereinafter, referred to as ‘a vertical GaN-based LED’) and a method of manufacturing the same, which can enhance reliability of an LED.
2. Description of the Related Art
Generally, a nitride-based semiconductor LED is grown on a sapphire substrate, but the sapphire substrate is a rigid nonconductor and has poor thermal conductivity. Therefore, there is a limitation in reducing the manufacturing costs by decreasing the size of a nitride-based semiconductor LED, or improving the optical power and chip characteristic. Particularly, because the application of a high current is essential for achieving high power LED, it is important to solve a heat-sink problem of the LED. To solve this problem, there has been proposed a vertical nitride-based LED in which a sapphire substrate is removed using a laser lift-off (LLO).
Hereinafter, the problems of a conventional GaN-based LED will be described in detail with reference to FIGS. 1A to 1F and 2.
FIGS. 1A to 1F are sectional views sequentially showing a method of manufacturing a conventional vertical GaN-based LED.
As shown in FIG. 1A, a light emission structure 120 composed of a GaN-based semiconductor layer is formed on a sapphire substrate 110. The light emission structure 120 includes an n-type GaN-based semiconductor layer 121, an active layer 122 composed of a GaN/InGaN layer with a multi-quantum well structure, and a p-type GaN-based semiconductor layer 123, which are sequentially laminated.
Subsequently, as shown in FIG. 1B, a plurality of positive electrodes (p-electrodes) 150 is formed on the p-type GaN-based semiconductor layer 123. Each of the p-electrodes 150 serves as an electrode and reflecting film.
Next, as shown in FIG. 1C, the light emission structure 120 is divided into units of LED through a RIE (reactive ion etching) process or the like.
Then, as shown in FIG. 1D, a protective film 140 is formed on the entire resulting structure such that the p-electrodes 150 are exposed. Next, a metal seed layer 160 is formed on the protective film 140 and the p-electrode 150, and electroplating or electroless plating is performed by using the metal seed layer 160 such that a structure support layer 170 composed of a plated layer is formed. The structure support layer 170 serves as a support layer and electrode of a finalized LED. At this time, the structure support layer 170 is also formed in a region between the light emission structures 120. Therefore, the structure support layer 170 formed in this region has a relatively large thickness.
Next, as shown in FIG. 1E, the sapphire substrate 110 is separated from the light emission structures 210 through an LLO process.
Subsequently, as shown in FIG. 1F, a negative electrode (n-electrode) 180 is formed on each of the n-type GaN-based semiconductor layers 121 exposed by separating the sapphire substrate 110. The structure support layer 170 is separated through a dicing or laser scribing process such that a plurality of GaN-based LEDs 100 is formed.
However, while the dicing or laser scribing of the structure support layer 170 having a relatively large thickness is performed, the light emission structure 120 may be broken or damaged.
Further, when the structure support layer 170 is formed, the overall structure including the structure support layer 170 is bent due to a difference in thermal expansion coefficient between the light emission structure 120 and the structure support layer 170 which is formed between the respective light emission structures 120. Therefore, it is not easy to perform a subsequent process.
Further, atoms composing the metal seed layer 160 penetrate into the active layer 122 such that junction leakage or a short circuit may occur.
As described above, when a vertical GaN-based LED is manufactured according to the related art, the reliability of the vertical GaN-based LED is degraded due to the above-described problems.
Meanwhile, another conventional vertical GaN-based LED can be manufactured according to a method to be described with reference to FIG. 2.
FIG. 2 is a sectional view illustrating the structure of another conventional vertical GaN-based LED.
As shown in FIG. 2, the vertical GaN-based LED has a structure support layer 270 formed in the lowermost portion thereof, the structure support layer 270 serving as a support layer of an LED. The structure support layer 270 may be formed of an Si substrate, a GaAs substrate, or a metal layer.
On the structure support layer 270, a bonding layer 260 and a reflecting electrode 250 are sequentially formed. Preferably, the reflecting electrode 250 is composed of metal with high reflectance so as to serve as an electrode and reflecting layer.
On the reflecting electrode 250, a p-type GaN-based semiconductor layer 240, an active layer 230 composed of a GaN/InGaN layer with a multi-quantum well structure, and an n-type GaN-based semiconductor layer 220 are sequentially formed.
On the n-type GaN-based semiconductor layer 220, an n-electrode 210 is formed. Between the n-type GaN-based semiconductor layer 220 and the n-electrode 210, a transparent electrode (not shown) may be further formed so as to enhance a current spreading effect.
In the conventional vertical GaN-based LED 200, the reflecting electrode 250 is formed on the entire surface of the p-type GaN-based semiconductor layer 240 such that light to be generated from the active layer 230 is reflected by the reflecting electrode 250 so as to escape to the outside. However, when the reflecting electrode 250 is formed on the entire surface of the p-type GaN-based semiconductor layer 240, a polarization effect occurs when the LED operates. Therefore, a piezoelectric effect occurs so that the reliability of the LED is degraded.